This invention relates to an endoprosthesis device for implantation within a body vessel, typically a blood vessel. More specifically, it relates to a tubular expandable stent of improved longitudinal flexibility.
Stents are placed or implanted within a blood vessel for treating stenoses, strictures or aneurysms therein. They are implanted to reinforce collapsing, partially occluded, weakened, or dilated sections of a blood vessel. They have also been implanted in the urinary tract and in bile ducts.
Typically, a stent will have an unexpanded (closed) diameter for placement and an expanded (opened) diameter after placement in the vessel or the duct. Some stents are self-expanding and some are expanded mechanically with radial outward force from within the stent, as by inflation of a balloon.
An example of the latter type is shown in U.S. Pat. No. 4,733,665 to Palmaz, which issued Mar. 29, 1988, and discloses a number of stent configurations for implantation with the aid of a catheter. The catheter includes an arrangement wherein a balloon inside the stent is inflated to expand the stent by plastically deforming it, after positioning it within a blood vessel.
A type of self-expanding stent is described in U.S. Pat. No. 4,503,569 to Dotter which issued Mar. 12, 1985, and discloses a shape memory stent which expands to an implanted configuration with a change in temperature. Other types of self-expanding stents not made of shape memory material are also known.
This invention is directed to stents of all these types when configured so as to be longitudinally flexible as described in detail hereinbelow. Flexibility is a desirable feature in a stent so as to conform to bends in a vessel. Such stents are known in the prior art. Examples are shown in U.S. Pat. No. 4,856,516 to Hillstead; U.S. Pat. No. 5,104,404 to Wolff; U.S. Pat. No. 4,994,071 to MacGregor; U.S. Pat. No. 5,102,417 to Palmaz; U.S. Pat. No. 5,195,984 to Schatz; U.S. Pat. No. 5,135,536 to Hillstead; U.S. Pat. No. 5,354,309 to Shepp-Pesch et al.; EPO Patent Application 0 540 290 A2 to Lau; EPO Patent Application No. 0 364 787 B1 to Schatz, and PCT Application WO 94/17754 (also identified as German Patent Application 43 03 181).
Generally speaking, these kinds of stents are articulated and are usually formed of a plurality of aligned, expandable, relatively inflexible, circular segments which are interconnected by flexible elements to form a generally tubular body which is capable of a degree of articulation or bending. Unfortunately, a problem with such stents is that binding, overlapping or interference can occur between adjacent segments on the inside of a bend due to the segments moving toward each other and into contact or on the outside of a bend the segments can move away from each other, leaving large gaps. This can lead to improper vessel support, vessel trauma, flow disturbance, kinking, balloon burst during expansion, and difficult recross for devices to be installed through already implanted devices and to unsupported regions of vessel.
A diamond configuration with diagonal connections between each and every diamond of each segment is also known but such closed configurations lack flexibility.
It is an object of this invention to provide a longitudinally flexible stent of open configuration that avoids these problems and exhibits improved flexibility (radially and longitudinally) in the stent body segments thereof rather than in flexible joints between the segments.
It is a further object of the present invention to provide a stent that is flexible yet also allows for side branch access.
It is a goal of the present invention to provide a flexible stent formed of interconnected bands which provides for side branch access and which further avoids the problem of pinching or overlap between adjacent bands. Pinching or overlap is avoided where peaks and troughs of adjacent bands are circumferentially displaced relative to each other. The stents of the present invention accomplish this goal by having different bands characterized by different wavelengths over the length of the stent and/or disposing the interconnecting members in such a way that after expansion of the stent, the phase relationship between adjacent bands is altered with the peaks and troughs displaced circumferentially relative to each other.
The inventive expandable stents are formed of a plurality of interconnected band-like elements characterized by alternating peaks and troughs. The ends of the interconnecting members which join adjacent bands are circumferentially offset and optionally, longitudinally offset. Peaks and troughs in adjacent bands are circumferentially offset as well so that the stent, in an expanded state, will have minimal overlap of peaks and troughs.
To this end, the invention provides a tubular, flexible, expandable stent, comprising a plurality of undulating band-like elements of a selected wavelength or wavelengths. The band-like elements have peaks and troughs and are aligned on a common longitudinal axis to define a generally tubular stent body. The peaks and troughs take a generally longitudinal direction along the stent body. Adjacent band-like elements may be in phase or out of phase with each other. The inventive stents further comprise a plurality of interconnecting elements having first ends and second ends. The first and second ends extend from adjacent band-like elements and are displaced from one another in a longitudinal direction and in a radial direction along the stent. Desirably, upon expansion of the stent, at least some of the peaks and troughs of a given band-like element are displaced relative to each other about the periphery of the stent to accommodate longitudinal flexing of the stent within the band-like elements and without interference between adjacent band-like elements.
In one embodiment, two different types of band-like elements are present in the stent, first band-like elements with a first selected wavelength and second band-like elements with a second selected wavelength exceeding the first selected wavelength. The first and second band-like elements preferably alternate over the length of the stent. Although the terminology of xe2x80x98first band-like elementxe2x80x99 and xe2x80x98second band-like elementxe2x80x99 is used, it is not intended to convey the relative order of appearance of the elements in the inventive stents.
In another embodiment, two different types of band-like elements are present, first and second band-like elements, each of which has peaks and troughs. The first band-like elements have more peaks (or troughs) than the second band-like elements. Similarly, the invention is also directed to embodiments having first and second band-like elements with peaks and troughs where the peaks (or troughs) of the first band-like elements are spaced closer together than the peaks (or troughs) of the second band-like elements.
In another embodiment in which band-like elements of only one wavelength are present, adjacent bands are about 180xc2x0 out of phase with one another. Interconnecting elements extend at an oblique angle relative to the longitudinal axis from a peak to a trough on an adjacent band.
In another embodiment in which band-like elements of only one wavelength are present, peaks from which interconnecting elements emanate are elongated relative to the peaks which are not connected to troughs and similarly, the troughs from which interconnectors emanate are elongated relative to troughs which are not connected to peaks. Further, each interconnecting element extends from the side of a peak to the side of a trough on an adjacent band.
In yet another embodiment in which band-like elements of only one wavelength are present, adjacent bands are about 90xc2x0 out of phase with one another. Each interconnecting element extends between a peak and a trough and the ends of the interconnecting member are circumferentially offset from one another and, optionally, longitudinally offset.
The invention further provides a tubular, flexible, expandable stent having a longitudinal axis, comprising one or more cylindrical shaped first segments having first struts, the first segment being defined by a member formed in an undulating pattern of interconnected paired first struts and in which adjacent pairs of first struts in a given first segment are interconnected at opposite ends and one or more cylindrical shaped second segments defined by a member formed in an undulating pattern of interconnected paired second struts and in which adjacent pairs of second struts in a given second segment are interconnected at opposite ends. The first struts are shorter than the second struts. The first segments are formed of a number of first struts and the second segments are formed of a number of second struts with the number of first struts in a first segment exceeding the number of second struts in a second segment. The first and second segments, present and desirably alternating along the stent body, are aligned on a common longitudinal axis to define a generally tubular stent body. Adjacent first and second segments are connected by a plurality of interconnecting elements, each interconnecting element extending from an end of paired first struts on a first segment to an end of paired second struts on an adjacent second segment. The ends of interconnecting elements are circumferentially offset relative to each other, and optionally, longitudinally offset. Desirably, upon expansion of the stent, the paired struts of the adjacent segments are displaced relative to each other about the periphery of the stent body to accommodate longitudinal flexing of the stent within the segments and without interference between adjacent segments.